Assessment of strict autumn-winter emission controls on air quality in the Beijing-Tianjin-Hebei region

Abstract. Strict seasonal emission controls are a popular measure in China for addressing severe air pollution, in particular fine particulate matter (PM2.5). Here we evaluate the efficacy of these measures, with a particular focus on the strict emission controls imposed on pollution sources in 28 cities in and around the Beijing-Tianjin-Hebei region (BTH) in autumn-winter 2017/2018. For this we use the GEOS-Chem chemical transport model and air pollutant measurements from the national and Beijing local monitoring networks, after evaluating the network data with independent measurements and correcting large biases in the bottom-up emissions inventory. The network measurements are temporally consistent (r > 0.9 for PM2.5 and r > 0.7 for gases) with the independent measurements, though with systematic differences of 5–17 % for nitrogen dioxide (NO2) and 16–28 % for carbon monoxide (CO). The average decrease in monitoring network PM2.5 in BTH in autumn-winter 2017/2018 relative to the previous year is 27 %, declining from 103 to 75 µg m−3. The regional decline in PM2.5 in the model is 20 %, exceeding the regional target of 15 %. According to the model, pollution control measures led to decline in PM2.5 precursor emissions of 0.27 Tg NOx (as NO), 0.66 Tg sulfur dioxide (SO2), 70 Gg organic carbon (OC), and 50 Gg black carbon (BC). We find though that these alone only lead to an 8 % decline in PM2.5 and that interannual variability in meteorology accounts for more than half (57 %) the decline. This demonstrates that year-on-year comparisons are misleading for assessing the efficacy of air pollution measures and should be taken into consideration when extending such measures beyond BTH.